1. Field of the Invention
The present invention relates to a toner for use in an image forming process such as an electrophotographic process or electrostatic printing process.
The present invention also relates to a method of forming an image, using a two-component developer comprising the above-mentioned toner and a magnetic carrier.
The present invention also relates to an image formation apparatus, using the two-component developer comprising the above-mentioned toner.
The present invention also relates to a container containing therein the above-mentioned toner.
The present invention also relates to an image formation apparatus equipped with the container containing therein the above-mentioned toner.
2. Discussion of Background
A dry type two-component developer for use in a two-component type development method comprises a carrier composed of relatively large particles (hereinafter referred to as the carrier particles), and a toner composed of fine particles (hereinafter referred to as the toner particles) which toner particles are triboelectrically held on the surface of the relatively large carrier particles.
When the developer comes near a latent electrostatic image, the attraction of the toner particles to the latent electrostatic image overcomes the bonding force between the toner particles and the carrier particles, so that the toner particles are attracted to the latent electrostatic image and deposited thereon, whereby the latent electrostatic image is developed to a visible toner image. The developer is repeatedly used with the replenishment of the toner thereto as the toner is consumed by the development of latent electrostatic images.
Conventional toners for use in two-component developers are mostly of a non-magnetic type, in which carbon black is used as a coloring agent. Such conventional toners have a shortcoming that the fogging of images is apt to be caused when the carrier serving as a charge application member deteriorates while in use, and applies to the toner particles electric charges with a polarity opposite to the polarity of electric charges that should be applied to the toner particles, or when the toner particles are not sufficiently charged by the carrier.
As a countermeasure against such a problem, there has been devised a method for preventing the occurrence of the fogging of images by containing a magnetic material in the toner and applying a magnetic bias thereto. However, when the amount of the magnetic material is excessive in the toner, images with a sufficient density for use in practice cannot be obtained so that an appropriate range of the amount thereof must be found, while when the amount of the magnetic material is small, carbon black must be used in combination with the magnetic material since the coloring is insufficient when only the magnetic material is used. However, in order to improve the coloring degree, a large amount of carbon black is used, there occurs a problem that the tolerance for the image fogging is reduced.
A heat roller system for application of heat application is widely and generally used as an image fixing system in electrophotography due to the advantage of energy efficiency thereof over other image fixing systems.
Recently, there is a tendency that thermal energy applied to the toner at the time of fixing toner images is reduced because of the recent development of the low-temperature image fixing and high speed copying for rational use of energy.
The improvement of the low-temperature image fixing performance of such a toner for use in the low-temperature image fixing has been generally tried by use of resins with low softening points and waxes. However, such toners for use in the low-temperature image fixing are vulnerable to heat, so that it is known that such toners are solidified by the heat applied mechanically or the heat applied during the storage thereof, which is known as the so-called blocking. Furthermore, it is difficult for such toners to attain a sufficient image fixing temperature range for use in practice. Such problems have not yet been solved even by use of polyester resin, which is said to have relatively good heat retention performance for its good low-temperature image fixing performance.
In order to solve these problems, there have been made several proposals to use two kinds of polyester resins with different characteristics in combination.
For example, in Japanese Laid-Open Patent Application No. 60-90344, there is proposed a method of mixing a non-linear polyester resin and a linear polyester resin.
In Japanese Laid-Open Patent Application No. 64-15755, there is proposed a method of mixing a cross-linked polyester resin with Tg of 50° C. or more and a softening point of 200° C. or less, and a straight chain polyester resin with a softening point of 150° C. or less and MW of 3,000 to 50,000.
In Japanese Laid-Open Patent Application No. 2-82267, there is proposed a method of containing a non-linear polyester resin with MW of 5,000 or more and a dispersion ratio of 20 or more, and a linear polyester resin with MW of 1,000 to 5,000 and a dispersion ratio of 4 or less.
In Japanese Laid-Open Patent Application No. 3-229264, there is proposed a method of containing an organometallic compound composed of a linear polyester resin with an acid value of 5 to 60 and a non-linear polyester resin with an acid value of less than 5.
In Japanese Laid-Open Patent Application No. 3-41470, there is proposed a method of mixing saturated polyester resins with the difference between the acid values thereof being 1.5 or more.
Due to the recent further developed low-temperature image fixing, a demand for more advanced low-temperature image fixing performance, and a significant reduction in size of image fixing unit, it is extremely difficult to secure a further advanced low-temperature image fixing performance, an extended image fixing temperature range, and thermal preservation performance at the same time when an image fixing unit which used a light load.
Furthermore, in the two-component development method, it is necessary that the mixing ratio of carrier and toner, namely, toner concentration, be constant in order to obtain a stable image density. In order to achieve this, it is necessary to mount a toner replenishing mechanism, a sensor and other devices on the image development unit. These devices make the development unit large and the operation thereof complex. These are the shortcomings of the two-component development method.
In contrast to this, in the mono-component development method, such a developer as composed of a mixture of carrier particles and toner particles is not used as in the two-component development method, but a toner composed of toner particles is held on a development sleeve by electric force generated triboelectrically between the toner and the development sleeve, or by magnetic force generated between a magnetic-material-containing toner and a magnet-built-in development sleeve, so that when the toner particles come near a latent electrostatic image, the attraction of the latent electrostatic image for the toner particles overcomes the bonding force between the toner particles and the development sleeve and the toner particles are deposited on the latent electrostatic image, whereby the latent electrostatic image is developed to a visible toner image.
Therefore, it is unnecessary to control the toner concentration in the mono-component development method and therefore the development unit for the mono-component development method can be advantageously reduced in size.
However, in the mono-component development, the number of toner particles in the development area is smaller than that in the development area in the two-component development, a sufficient amount of toner cannot be supplied to a photoconductor in the mono-component development method and therefore it has been difficult to apply the mono-component development method to a high speed copying machine.
In contrast to the above, there is known a development unit which is capable of incorporating the toner into the two-component developer in accordance with the movement of the developer, without the necessity for a toner concentration detector. This development unit, however, has the shortcoming that the amount of the toner incorporated differs in the place where the developer moves actively, and in the place where the developer does not move actively, and also in the place where there is a large amount of the developer and in the place where there is not much developer, making places where the toner concentration is partially non-uniform, thus, non-uniform image density and toner deposition on the background of images are apt to be caused.
In order to solve the above-mentioned problems, in Japanese Laid-Open Patent Application No. 63-4282, there is disclosed a method of disposing two toner replenishing members within a toner hopper so as to allow the developer to pass through the routes formed by the two toner replenishing members, whereby non-uniform image density and the deposition of the toner on the background of images in the longitudinal direction of the development unit are prevented.
The above disclosed method, however, has the shortcomings that the use of the two toner replenishing members makes the development unit large and expensive.
In Japanese Laid-Open Patent Application No. 9-197833, there is disclosed a method of eliminating the problems in the above-mentioned method. However, the method disclosed therein is not yet capable of completely solving the problem of the non-uniform image density.
Furthermore, in recent years, higher image quality is demanded on the market, and the demand cannot be met by use of a conventional toner with a volume mean particle diameter of 10 μm to 15 μm. There is a keen customer demand for a toner with a smaller particle diameter.